1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly to an eccentric coupling device in a radial compliance scroll compressor, which is capable of preventing abnormal behavior of an eccentric bush caused by a pressure difference between upper and lower ends of the eccentric bush during operation of the scroll compressor, while preventing the eccentric bush from rising axially.
2. Description of the Related Art
Generally, a scroll compressor includes upper and lower scrolls respectively provided with involute-shaped wraps engaged with each other. One of the scrolls performs an orbiting motion with respect to the other scroll to reduce the volume of spaces defined between the scrolls, thereby compressing gas confined in the spaces.
As such a conventional compressor, a radial compliance scroll compressor is known. In such a radial compliance scroll compressor, an orbiting scroll thereof is backwardly moved when liquid refrigerant, oil or foreign matter is introduced into compression chambers defined between the orbiting scroll and the other scroll, that is, a fixed scroll, thereby abnormally increasing the gas pressure in the compression chambers. In accordance with the backward movement of the orbiting scroll, it is possible to prevent the wraps of the scrolls from being damaged due to the abnormally increased gas pressure.
FIG. 1 is a sectional view illustrating the entire configuration of a conventional radial compliance scroll compressor.
As shown in FIG. 1, the conventional radial compliance scroll compressor includes a shell 1, and main and sub frames 2 and 3 respectively arranged in the shell 1 at upper and lower portions of the shell 1. A stator 4, which has a hollow structure, is interposed between the main and sub frames 2 and 3 within the shell 1.
A rotor 5 is arranged inside the stator 4 such that it rotates when current flows through the stator 4. A vertical crankshaft 6 extends axially through a central portion of the rotor 5 while being fixed to the rotor 5 so that it is rotated along with the rotor 5. The crankshaft 6 has upper and lower ends protruded beyond the rotor 5, and rotatably fitted in the main and sub frames 2 and 3, respectively. Thus, the crankshaft 6 is rotatably supported by the main and sub frames 2 and 3.
An orbiting scroll 7 is mounted to an upper surface of the main frame 2 in the shell 1. The orbiting scroll 7 is coupled, at a lower portion thereof, with the upper end of the crankshaft 6, which is protruded through the main frame 2, so that it performs an orbiting motion in accordance with rotation of the crankshaft 6. The orbiting scroll 7 is provided, at an upper portion thereof, with an orbiting wrap 7a having an involute shape. The orbiting wrap 7a extends upwardly from an upper surface of the orbiting scroll 7. A fixed scroll 8 is arranged on the orbiting scroll 7 in the shell 1 while being fixed to the shell 1. The fixed scroll 8 is provided, at a lower portion thereof, with a fixed wrap 8a adapted to be engaged with the orbiting wrap 7a of the orbiting scroll 7 such that compression chambers 22 are defined between the wraps 7a and 8a. With this configuration, when the orbiting scroll 7 performs an orbiting motion in accordance with rotation of the crankshaft 6, gaseous refrigerant is introduced into the compression chambers 22 in a sequential fashion, so that it is compressed.
For the orbiting motion thereof, the orbiting scroll 7 is eccentrically coupled to the crankshaft 6. For this eccentric coupling, the crankshaft 6 is provided with a crank pin 10 upwardly protruded from the upper end of the crankshaft 6 at a position radially spaced apart from the center of the upper end of the crankshaft 6 by a certain distance. Also, the orbiting scroll 7 is provided, at the lower portion thereof, with a boss 7b centrally protruded from a lower surface of the orbiting scroll 7.
A bearing 11 is forcibly fitted in the boss 7b. Also, an eccentric bush 12 is rotatably fitted around the crank pin 10. The crank pin 10 of the crankshaft 6 is rotatably received in the boss 7b of the orbiting scroll 7 via the bearing 11 and eccentric bush 12, so that the orbiting scroll 7 is eccentrically coupled to the crankshaft 6.
As a rotation preventing mechanism for the orbiting scroll 7, an Oldham ring 9 is arranged between the main frame 2 and the orbiting scroll 7. An oil passage 6a extends vertically throughout the crankshaft 6. Upper and lower balance weight members are provided at upper and lower surfaces of the rotor 5, respectively, in order to prevent a rotation unbalance of the crankshaft 6 caused by the crank pin 10.
In FIG. 1, reference numerals 15 and 16 designate suction and discharge pipes, respectively, reference numerals 17 and 18 designate a discharge port and a discharge chamber, respectively, reference numeral 19 designates a check valve, reference numeral 20 designates oil, and reference numeral 21 designates an oil propeller.
When current flows through the stator 4, the rotor 5 is rotated inside the stator 4, thereby causing the crankshaft 6 to rotate. In accordance with the rotation of the crankshaft 6, the orbiting scroll 7 coupled to the crank pin 10 of the crankshaft 6 performs an orbiting motion with an orbiting radius defined between the center of the crankshaft 6 and the center of the orbiting scroll 7.
In accordance with a continued orbiting motion of the orbiting scroll 7, the compression chambers 22, which are defined between the orbiting wrap 7a and the fixed wrap 8a, are gradually reduced in volume, so that gaseous refrigerant sucked into each compression chamber 22 via the suction pipe 15 is compressed to high pressure. The compressed high-pressure gaseous refrigerant is subsequently discharged into the discharge chamber 18 via the discharge port 17. The compressed high-pressure gaseous refrigerant is then outwardly discharged from the discharge chamber 18 via the discharge pipe 16.
Meanwhile, when an abnormal increase in pressure occurs in the compression chambers 22 due to introduction of liquid refrigerant, oil or foreign matter into the compression chambers 22, the orbiting scroll 7 is radially shifted such that the orbiting wrap 7a is moved away from the fixed wrap 8a, due to the abnormally increased pressure. As a result, it is possible to prevent the wraps 7a and 8a from being damaged by the abnormally increased pressure.
In the radial compliance scroll compressor having the above mentioned configuration, the eccentric bush 12 is coupled to the crank pin 10 in the above mentioned manner, in order to vary the orbiting radius of the orbiting scroll 7. Also, the eccentric bush 12 generates a centrifugal force corresponding to an eccentricity thereof, that is, the distance between the center of the crank pin 10 and the center of the eccentric bush 12, during the orbiting motion of the orbiting scroll 7. By virtue of this centrifugal force, the eccentric bush 12 can perform a sealing function for the compression chambers 22.
FIG. 2 is an exploded perspective view illustrating a structure of the conventional eccentric bush.
As shown in FIG. 2, the eccentric bush 12 has a crank pin hole 12b so that it is rotatably fitted around the crank pin 10. When an abnormal increase in pressure occurs in the compression chambers 22, the eccentric bush 12 is rotated such that the orbiting scroll 7 is radially shifted to cause the orbiting wrap 7a to be moved away from the fixed wrap 8a. 
In order to limit the rotation of the eccentric bush 12 to a predetermined angle, the crank pin 10 has a cutout having a D-shaped cross-section, and thus, a cut surface 10a, at one side thereof. The eccentric bush 12 also has a stopper hole 12a at one side of the crank pin hole 12b. A cylindrical stopper 23 is fitted in the stopper hole 12a. The stopper hole 12a is arranged such that it overlaps with the crank pin hole 12b, so that the cylindrical stopper 23 fitted in the stopper hole 12a is radially protruded into the crank pin hole 12b. 
FIGS. 3a and 3b are cross-sectional views respectively illustrating different operation states of the eccentric bush shown in FIG. 2.
At a normal position of the eccentric bush 12, the stopper 23 is spaced apart from the cut surface 10a, as shown in FIG. 3a. 
When the eccentric bush 12 is rotated, as indicated by an arrow in FIG. 3b, the stopper 23 is rotated, along with the eccentric bush 12, so that it comes into contact with the cut surface 10a. Thus, the rotation of the eccentric bush 12 is limited to a certain range.
Meanwhile, oil is fed to the upper end of the eccentric bush 12 through the oil passage 6a of the crankshaft 6, and then dispersed from the upper end of the eccentric bush 12 to perform a function of lubricating contact portions of the bearing 11 and eccentric bush 12. However, there may be a difference between the amounts of oil respectively supplied to the upper and lower portions of the eccentric bush 12.
Such an oil supply amount difference may generate friction between the bearing 11 and the eccentric bush 12 at the lower portion of the eccentric bush 12. Such friction may cause the eccentric bush 12 to rise axially.
The eccentric bush 12 has an inner peripheral surface roughly machined as compared to an outer peripheral surface thereof to be in slidable contact with the bearing 11. Due to the roughness of the inner peripheral surface of the eccentric bush 12, increased friction is generated between the eccentric bush 12 and the crank pin 10. For this reason, the eccentric bush 12 exhibits abnormal behavior. For example, the eccentric bush 12 may be repeatedly moved in upward and downward directions without being maintained at a fixed vertical position as it is repeatedly rotated in forward and backward directions during operation of the scroll compressor. Due to such abnormal behavior, the eccentric bush 12 may be axially elevated.
When the eccentric bush 12 is axially elevated due to various causes including a self-moment thereof, the contact area between the eccentric bush 12 and the crank pin 10 is reduced by the elevation length of the eccentric bush 12.
For this reason, a tilting phenomenon may occur. That is, the eccentric bush 12 may be upwardly moved in a state of being inclined to one side thereof. Such a tilting phenomenon causes an increase in the frictional force generated between the eccentric bush 12 and the bearing 11. As a result, the mechanism of the scroll compressor may be damaged. Furthermore, the performance of the scroll compressor may be degraded.